222 research outputs found
THE CHANGING PHYSIOLOGY OF MIDDLE AGE
It is not easy to talk sensibly about middle age because there is real doubt as to whether it exists. It is something which rapidly recedes from us as we approach it and at the other end it blends confusingly into old age. During this century improvements in medical care and a general increase in living standards have led people to expect to retain good health until quite late in life. It is now unusual for a physician to attribute any illness merely to old age and he would be most unwise to do so in a patient under the age of 70
Cross-Newell equations for hexagons and triangles
The Cross-Newell equations for hexagons and triangles are derived for general
real gradient systems, and are found to be in flux-divergence form. Specific
examples of complex governing equations that give rise to hexagons and
triangles and which have Lyapunov functionals are also considered, and explicit
forms of the Cross-Newell equations are found in these cases. The general
nongradient case is also discussed; in contrast with the gradient case, the
equations are not flux-divergent. In all cases, the phase stability boundaries
and modes of instability for general distorted hexagons and triangles can be
recovered from the Cross-Newell equations.Comment: 24 pages, 1 figur
Spin Ordering and Quasiparticles in Spin Triplet Superconducting Liquids
Spin ordering and its effect on low energy quasiparticles in a p-wave
superconducting liquid are investigated. We show that there is a new 2D p-wave
superconducting liquid where the ground state is rotation invariant. In quantum
spin disordered liquids, the low energy quasiparticles are bound states of the
bare Bogolubov- De Gennes ({\em BdeG}) quasiparticles and zero energy
skyrmions, which are charge neutral bosons at the low energy limit. Further
more, spin collective excitations are fractionalized ones carrying a half spin
and obeying fermionic statistics. In thermally spin disordered limits, the
quasi-particles are bound states of bare {\em BdeG} quasi-particles. The
latter situation can be realized in some layered p-wave superconductors where
the spin-orbit coupling is weak.Comment: 5 pages, no figures; published versio
Dual Vortex Theory of Strongly Interacting Electrons: Non-Fermi Liquid to the (Hard) Core
As discovered in the quantum Hall effect, a very effective way for
strongly-repulsive electrons to minimize their potential energy is to aquire
non-zero relative angular momentum. We pursue this mechanism for interacting
two-dimensional electrons in zero magnetic field, by employing a representation
of the electrons as composite bosons interacting with a Chern-Simons gauge
field. This enables us to construct a dual description in which the fundamental
constituents are vortices in the auxiliary boson fields. The resulting
formalism embraces a cornucopia of possible phases. Remarkably,
superconductivity is a generic feature, while the Fermi liquid is not --
prompting us to conjecture that such a state may not be possible when the
interactions are sufficiently strong. Many aspects of our earlier discussions
of the nodal liquid and spin-charge separation find surprising incarnations in
this new framework.Comment: Modified dicussion of the hard-core model, correcting several
mistake
Direct evidence of soft mode behavior near the Burns' temperature in PbMgNbO (PMN) relaxor ferroectric
Inelastic neutron scattering measurements of the relaxor ferroelectric
PbMgNbO (PMN) in the temperature range
490~KT880~K directly observe the soft mode (SM) associated with the
Curie-Weiss behavior of the dielectric constant (T). The results
are treated within the framework of the coupled SM and transverse optic (TO1)
mode and the temperature dependence of the SM frequency at q=0.075 a* is
determined. The parameters of the SM are consistent with the earlier estimates
and the frequency exhibits a minimum near the Burns temperature (
650K)Comment: 6 figure
Disorder Induced Phases in Higher Spin Antiferromagnetic Heisenberg Chains
Extensive DMRG calculations for spin S=1/2 and S=3/2 disordered
antiferromagnetic Heisenberg chains show a rather distinct behavior in the two
cases. While at sufficiently strong disorder both systems are in a random
singlet phase, we show that weak disorder is an irrelevant perturbation for the
S=3/2 chain, contrary to what expected from a naive application of the Harris
criterion. The observed irrelevance is attributed to the presence of a new
correlation length due to enhanced end-to-end correlations. This phenomenon is
expected to occur for all half-integer S > 1/2 chains. A possible phase diagram
of the chain for generic S is also discussed.Comment: 6 Pages and 6 figures. Final version as publishe
Inelastic scattering of 9Li and excitation mechanism of its first excited state
The first measurement of inelastic scattering of 9Li from deuterons at the ISAC facility is reported.
The measured angular distribution for the first excited state confirms the nature of excitation to be
an E2 transition. The quadrupole deformation parameter is extracted from an analysis of the angular
distribution.Web of Scienc
One-dimensional spin-1/2 Heisenberg antiferromagnet in a weak external magnetic field
The one dimensional spin-1/2 Heisenberg antiferromagnet in a weak magnetic
field h is studied using the bosonization method. We derive a set of
renormalization group equations. The fixed point is reached when the field is
scaled to the value at which the system is quarter-filled. As the magnetic
field varies, a continuum line of fixed points is formed. We compute the
uniform longitudinal susceptibility . The singular behavior of
as is found to be contained in with a
non-universal constant. The spin-spin correlations in the magnetic field are
calculated.Comment: 5 pages, 1 figure, published on PR
Low-energy fixed points of random Heisenberg models
The effect of quenched disorder on the low-energy and low-temperature
properties of various two- and three-dimensional Heisenberg models is studied
by a numerical strong disorder renormalization group method. For strong enough
disorder we have identified two relevant fixed points, in which the gap
exponent, omega, describing the low-energy tail of the gap distribution,
P(Delta) ~ Delta^omega is independent of disorder, the strength of couplings
and the value of the spin. The dynamical behavior of non-frustrated random
antiferromagnetic models is controlled by a singlet-like fixed point, whereas
for frustrated models the fixed point corresponds to a large spin formation and
the gap exponent is given by omega ~ 0. Another type of universality classes is
observed at quantum critical points and in dimerized phases but no infinite
randomness behavior is found, in contrast to one-dimensional models.Comment: 11 pages RevTeX, eps-figs included, language revise
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